The present invention relates to the improvement of an interlayer dielectric film in a semiconductor device which has a multi-layer wiring structure having wiring layers of copper.
In order to achieve the high-density integration of semiconductor devices, it has been developed to provide devices, such as the scale down of patterns and the multilayering of circuits. As one of such devices, there is a technique for multilayering the wiring layers. In order to provide a multi-layer wiring structure, a number n wiring layer and a number (n+1) wiring layer are connected to each other by means of a conductive layer, and a thin film called an interlayer dielectric film is formed in a region other than the conductive layer.
In general, an SiO2 film is used as the interlayer dielectric film, and an aluminum (Al) layer is used as the wiring layer. However, if the wiring layer of Al is used, its resistance increases in accordance with the scale down of patterns, so that there is a problem in that the fall of potential in a power supply line and the delay of clock signals are uneven to cause malfunction. Since current density flowing through the wiring increases, there is also a problem in that the wiring is broken by electro-migration to deteriorate reliability.
Therefore, it has been studied that copper (Cu), which has a lower resistance than that of Al and which is resistant to electro-migration, is used as the material of the wiring. In this case, since it is difficult to etch Cu, a process utilizing, e.g., the chemical mechanical polishing (CMP) method, is carried out, i.e., Cu is deposited in a hole or groove formed in an insulating film, and then, the CMP is carried out to flatten the surface of the insulating film to form a pattern wiring.
However, Cu is easy to diffuse in silicon (Si) and the SiO2 film. For that reason, when the SiO2 film is used as the insulating film and Cu is used as the material of the wiring, the junction leak of the semiconductor device, the dielectric breakdown of a gate oxide film, and the fluctuation in MOS threshold voltage are caused to have a bad influence on the performance of the semiconductor device.
Therefore, when Cu is used as the material of the wiring layer, it has studied that a barrier film 13 having a thickness of, e.g., about 200 angstroms, is formed between an insulating film 11 and a Cu wiring layer 12 as shown in, e.g., FIG. 17, in order to prevent Cu from diffusing in the semiconductor device. It is considered that Ta, W, TiW, TiSi2, TiN, Ta2N, W2N, Ni0.6, N0.4, or amorphous Taxe2x80x94Sixe2x80x94N is used as the material of the barrier film. However, there is a problem in that the producing process for forming the barrier film 13 is complicated, and there is a problem in that it is difficult to select each material of the barrier film 13 since the material of the barrier film 13 has its merits and demerits, respectively.
On the other hand, it also has been studied that the insulating film is formed of a material, in which Cu is difficult to diffuse, in place of the formation of the barrier film. In general, the interlayer dielectric film is formed as an SiOF film, a polyimide film, a PSI (polyimide siloxane) film, a PAE (polyaryleneethers) film, a HSQ (hydrogen silsesquioxanes (H3Si3O12)) film or a BCB (benzocyclobutene) film, in place of the SiO2 film.
Although it is said that cu does not diffuse in the BCB film of the BCB polymer among these insulating films, it is confirmed that Cu diffuses in the Sio2 film, SiOF film, polyimide film and PSI film. The presence of diffusion of Cu in the PAE film and HSQ film has not been confirmed.
By the way, in recent years, in order to further accelerate the operation of the semiconductor device, it is required to lower the relative dielectric constant of the interlayer dielectric film. That is, the relative dielectric constant of the above described BCB film is about 2.7, so that it is desired to use a material, which has a smaller relative dielectric constant than that of the BCB film and in which Cu does not diffuse, as the insulating film.
The present invention has been made in such circumstances, and it is an object of the present invention to provide a semiconductor device capable of inhibiting Cu, which is the material of a wiring layer, from diffusing in an insulating film by forming the insulating film of a smaller relative dielectric constant than that of the BCB film.
In order to accomplish this object, according to the present invention, a semiconductor device comprises: a substrate; an insulating film of a fluorine-contained carbon film formed on the substrate; and a wiring layer of copper formed on the insulating film.
According to such a semiconductor device, by forming the insulating film of a CF film, it is possible to prevent copper, which is the material of the wiring layer, from diffusing into the insulating film, and the relative dielectric constant of the CF film can be smaller than that of a BCB film.
An adhesion layer may be formed between the insulating film and the wiring layer in order to prevent the wiring layer from being peeled off from the insulating film. In that case, the adhesion layer may comprise a metal layer of a metal, such as titanium, and a layer of a compound which contains carbon and the metal.
In such a semiconductor device, the insulating film is preferably amorphous. From the point of view of further prevention of copper diffusion, the insulating film preferably has a film density of 1.50 g/cm3. From the same point of view, the concentration of oxygen in the insulating film is preferably 3 atomic % or less, and the concentration of boron in the insulating film is preferably in the range of from 10xe2x88x923atomic % to 1 atomic %. Moreover, from the point of view of the improvement of hardness and heat resistance of the insulating film, nitrogen is effectively added, and the concentration of nitrogen in the insulating film is preferably 3 atomic % or less.